1. Field of the Invention
The invention relates to a cellulose-based sponge cloth which has been provided with an internal reinforcement and to a process for producing same. The sponge cloth is highly water-absorbent and is useful in the household and industry for various cleaning and decontaminating purposes.
2. Description of Related Art
Sponge cloth production by the viscose process is well known. First, pulp, especially wood pulp, is converted with sodium hydroxide and carbon disulfide into an alkaline cellulose xanthate solution known as viscose. At the same time, cotton noils are degreased with dilute, detergent-containing NaOH. The ripened viscose solution is then mixed with cotton fibers. This is generally done with the aid of a kneader. Instead of cotton fibers it is also possible to use viscose fibers as internal reinforcement. Glauber's salt (=sodium sulfate decahydrate) is then added and likewise mixed in uniformly. This sponge cloth raw material is then applied to a support, for example a foraminous endless belt, to whichever depth is desired. It is also possible to apply a mixture of viscose solution and Glauber's salt to a plastic support material, for example a net of polyethylene terephthalate (PET). The regeneration of the cellulose then takes place in a heated, alkaline coagulation bath. It can also be carried out in an acidic medium, for example dilute sulfuric acid. In the process, the internal reinforcement becomes integrated into the sponge cloth body.
Glauber's salt has a very low melting point. It therefore melts in the coagulation bath and is dissolved out. The disappearing salt crystals leave pores and voids behind. Finally, the sponge cloth is washed out to rid it of salt residues and adhering reaction products. After drying, it is cut into narrow lengths, which in turn are rolled up. The roll material can then be end-itemed into cloths of the desired size.
However, the viscose process is technically very complicated and costly. In addition, appreciable efforts are needed if it is not to impact adversely on the environment. An unpleasant concomitant of the viscose process is for example the formation of foul smelling hydrogen sulfide. A sponge cloth produced by the viscose process still contains residues of CS2 or H2S, which have to be expensively washed out. In addition, in the course of the several hours of ripening of the viscose solution, the cellulose polymer chains are more or less degraded. This leads to a pronounced broadening of the distribution curve of the degree of polymerization (DP) of the cellulose chains. Even the use of a cellulose starting material having the same degree of polymerization therefore does not consistently guarantee the same post-regeneration result. The mechanical stability of the sponge cloth will then moreover fluctuate, inter alia according to the degree of polymerization.
WO 97/42259 discloses sponge cloths containing reinforcing fibers and processes for producing them. The fibers can be added as additive or else originate from the cellulosic starting material if this is only incompletely dissolved. The dissolving of the cellulose material, which is pretreated with steam under high pressure, is generally effected using strongly alkaline, aqueous solutions, preferably with NaOH solutions. As well as a pore former, a blowing agent is additionally used as well at all times, for example a surfactant such as sodium lauryl sulfate.
EP-A 712 889 discloses fiber-containing cellulose/amine oxide solutions for producing mainly fibers, papers, films and food casings. Sponges are mentioned as well, but not sponge cloths.
WO 97/23552 describes cellulose sponges (not sponge cloths) and processes for producing them. These sponges are produced from a cellulose/NMMO solution which is mixed with a pore former and a blowing agent. The mixture is subsequently exposed to conditions under which the blowing agent decomposes, causing the cellulose solution to foam. This produces the large pores which are typical of sponges and which are undesirable in a sponge cloth.